At present, in quantum communication or some extreme cases, a receiver of a communication system may only receive communication light at the single-photon level. The extreme communication may be, for example, ultra-distance interstellar communication, satellite-ground communication in adverse weather conditions and underwater communication highly sensitive to loss and noise, etc. In the prior art, information may be encoded on the intensity of communication light, and when received communication light is at the single-photon level, information decoding may be performed by extending the integration time of photon counting.
However, in the prior art, a signal-to-noise ratio of photon counting may be very low due to shot noise at the single-photon level within short integration time. Therefore, to meet requirements of signal-to-noise for photon counting at a receiving terminal, it is necessary to maintain a long integration time. Therefore, in existing communication technologies, the channel capacity may be extremely low when a receiver of a communication system may only receive communication light at the single-photon level due to the long integration time.